"It's not too late to mend" comes from "The Warring States Policy Chu Ce": "It's not too late to see a rabbit love a dog; It is never too late to mend. It means it's not too late to mend the sheepfold if the sheep are lost. Figuratively speaking, finding a way to remedy the problem can prevent further losses. " If you realize what you have done in the past, don't remonstrate, and those who know can catch up "means that I finally realize that what I did wrong in the past cannot be corrected;" At the same time, I realize that the future can be saved. "Cold corner has gone, mulberry is not too late" means that the early years have gone. If you cherish time and make efforts, it's not too late to be old.